Aging is the single most important risk factor for Alzheimer's disease (AD), which represents the most common cause of dementia in the world. Our group has shown that a naturally occurring switch from the TrkA to the p75 neurotrophin receptor system is responsible for the activation of amyloid p-peptide (A[3) that characterizes aging. Such an event occurs downstream of the aging program mediated by the insulin-like growth factor 1 receptor (IGF1-R), and leads to activation of neutral sphingomyelinase (nSMase), the enzyme that generates the lipid second messenger ceramide. Ceramide, in turn, is responsible for the molecular stabilization of BACE1 and the increased production of Ap. The above events can be blocked by genetic and biochemical approaches that target IGF1-R, p75NTR, or nSMase. In the Preliminary Studies Section, we report that ceramide regulates a transient form of lysine acetylation of nascent BACE1 that affects the molecular stability of the p secretase. This process involves lysine acetylation in the lumen of the ER/ERGIC and is followed by deacetylation in the lumen of the Golgi apparatus, once the nascent protein is fully mature. Given the role that BACE1 plays in the molecular pathogenesis of AD, our results have profound implications for the neurobiology of the disease. The central hypothesis of this proposal is that ceramide is the last output of a signaling pathway that controls AD-neuropatholoqy during aging. Specifically, we propose that ceramide regulates AB generation by affecting the acetylation and molecular stability of BACE1, the rate-limiting enzyme for the biogenesis of Ap. Specific Aim 1 will study the biochemical properties of the acetyl-CoA membrane transporter, which translocates acetylCoA from the cytosol to the lumen of the ER, where it serves as donor of acetyl groups for the molecular stabilization of BACE1. Specific Aim 2 will study the function and biochemical properties of two newly-identified acetylCoA:lysine acetyltransferases that are required for the molecular stabilization of BACE1, downstream of ceramide. For the execution of the above two Specific Aims, we have described a combination of biochemical and genetic approaches. The biochemical approaches include enzymatic assays, in vitro reconstitution, affinity purification, subcellular fractionation studies, and depletion studies. The genetic approaches include stable transfection and "gene-silencing" of the above targets. Finally, translational research is described as part of our proposal to translate our findings into novel therapeutic approaches to prevent late-onset AD. RELEVANCE (See instructions): Aging is the single most important risk factor for Alzheimer's disease (AD). Because of the increase in life expectancy that we are experiencing, AD is predicted to affect 45 million individuals worldwide by the year 2050. We have identified a novel molecular pathway that links aging to AD neuropathology. The long-term objective of this proposal is to characterize this pathway and design new approaches for the prevention of AD.